struct-buffer

Add structure to ArrayBuffer

Install

$ npm i struct-buffer

how to use

import { float, string_t, StructBuffer, pack } from "struct-buffer";

const struct = new StructBuffer("Player", {
  hp: float,
  mp: float,
  name: string_t[3],
});

const buffer: DataView = pack("2f3s", 10, 100, "abc");

// decode
const data = struct.decode(buffer);
// data => { hp: 10, mp: 100, name: 'abc' }

// encode
const view = struct.encode({
  hp: 10,
  mp: 100,
  name: "abc",
});
// view => <41 20 00 00 42 c8 00 00 61 62 63>

Use in browser

<script src="struct-buffer.js"></script>
<script>
  const { DWORD, string_t, StructBuffer, uint32_t } = window.StructBuffer;
</script>

Use "type" for conversion

import { DWORD } from "struct-buffer";

// encode
const view = DWORD[2].encode([1, 2]); 
// view => <00 00 00 01 00 00 00 02>

// decode
const data = DWORD[2].decode(view);
// data => [ 1, 2 ]

register Type

const myShort = registerType("short", 2, false);

const struct = new StructBuffer("Player", {
  hp: myShort,
  mp: myShort,
  pos: myShort[2],
});

// encode
const view = struct.encode({
  hp: 2,
  mp: 10,
  pos: [100, 200],
});
// view => <00 02 00 0a 00 64 00 c8>

// decode
const data = struct.decode(view);
// data => { hp: 2, mp: 10, pos: [ 100, 200 ] }

typedef

const HANDLE = typedef("HANDLE", DWORD);
HANDLE.size // 4
HANDLE.unsigned // true

Nested struct

/*
typedef struct _XINPUT_STATE {
  DWORD          dwPacketNumber;
  XINPUT_GAMEPAD Gamepad;
} XINPUT_STATE, *PXINPUT_STATE;


typedef struct _XINPUT_GAMEPAD {
  WORD  wButtons;
  BYTE  bLeftTrigger;
  BYTE  bRightTrigger;
  SHORT sThumbLX;
  SHORT sThumbLY;
  SHORT sThumbRX;
  SHORT sThumbRY;
} XINPUT_GAMEPAD, *PXINPUT_GAMEPAD;
*/

XINPUT_GAMEPAD = new StructBuffer("XINPUT_GAMEPAD", {
  wButtons: WORD,
  bLeftTrigger: BYTE,
  bRightTrigger: BYTE,
  sThumbLX: int16_t,
  sThumbLY: int16_t,
  sThumbRX: int16_t,
  sThumbRY: int16_t,
});

XINPUT_STATE = new StructBuffer("XINPUT_STATE", {
  dwPacketNumber: DWORD,
  Gamepad: XINPUT_GAMEPAD,
});

// decode
XINPUT_STATE.decode(
    new Uint8Array([
      0, 0, 0, 0, // dwPacketNumber
      0, 1, // wButtons
      0,    // bLeftTrigger
      0,    // bRightTrigger
      0, 1, // sThumbLX
      0, 2, // sThumbLY
      0, 3, // sThumbRX
      0, 4, // sThumbRY
    ])
);

// encode
XINPUT_STATE.encode({
  dwPacketNumber: 0,
  Gamepad: {
    wButtons: 1,
    bLeftTrigger: 0,
    bRightTrigger: 0,
    sThumbLX: 1,
    sThumbLY: 2,
    sThumbRX: 3,
    sThumbRY: 4,
  },
});

parse c-struct

import { CStruct } from "struct-buffer";

const cStruct = `
//
// Structures used by XInput APIs
//
typedef struct _XINPUT_GAMEPAD
{
    WORD                                wButtons;
    BYTE                                bLeftTrigger;
    BYTE                                bRightTrigger;
    SHORT                               sThumbLX;
    SHORT                               sThumbLY;
    SHORT                               sThumbRX;
    SHORT                               sThumbRY;
} XINPUT_GAMEPAD, *PXINPUT_GAMEPAD;

typedef struct _XINPUT_STATE
{
    DWORD                               dwPacketNumber;
    XINPUT_GAMEPAD                      Gamepad;
} XINPUT_STATE, *PXINPUT_STATE;

typedef struct _XINPUT_VIBRATION
{
    WORD                                wLeftMotorSpeed;
    WORD                                wRightMotorSpeed;
} XINPUT_VIBRATION, *PXINPUT_VIBRATION;

typedef struct _XINPUT_BATTERY_INFORMATION
{
    BYTE BatteryType;
    BYTE BatteryLevel;
} XINPUT_BATTERY_INFORMATION, *PXINPUT_BATTERY_INFORMATION;
`;

const structs = CStruct.parse(cStruct);
sizeof(structs.XINPUT_GAMEPAD) // 12
sizeof(structs.XINPUT_STATE) // 16
sizeof(structs.XINPUT_VIBRATION) // 4
sizeof(structs.XINPUT_BATTERY_INFORMATION) // 2

struct list

const User = new StructBuffer("User", {
  name: string_t[2],
  name2: string_t[2],
});

const Users = new StructBuffer("Users", {
  users: User[2],
});

const data = Users.decode(
  new Uint8Array([0x61, 0x31, 0x61, 0x32, 0x62, 0x31, 0x62, 0x32])
);
// data.users.length => 2
// data.users[0] => { name: "a1", name2: "a2" }
// data.users[1] => { name: "b1", name2: "b2" }

// or

const users = User[2].decode(
  new Uint8Array([0x61, 0x31, 0x61, 0x32, 0x62, 0x31, 0x62, 0x32])
);
// users => [ { name: 'a1', name2: 'a2' }, { name: 'b1', name2: 'b2' } ]

StructBuffer to c-struct

import { CStruct } from "struct-buffer";

const XINPUT_GAMEPAD = new StructBuffer("XINPUT_GAMEPAD", {
  wButtons: WORD,
  bLeftTrigger: BYTE,
  bRightTrigger: BYTE,
  sThumbLX: int16_t,
  sThumbLY: int16_t,
  sThumbRX: int16_t,
  sThumbRY: int16_t[2],
});
const cStruct = CStruct.from(XINPUT_GAMEPAD);

// console.log(cStruct) => 
typedef struct _XINPUT_GAMEPAD
{
    WORD wButtons;
    BYTE bLeftTrigger;
    BYTE bRightTrigger;
    int16_t sThumbLX;
    int16_t sThumbLY;
    int16_t sThumbRX;
    int16_t sThumbRY[2];
} XINPUT_GAMEPAD, *XINPUT_GAMEPAD;

"string_t" Truncate when encountering 0

string_t[4].decode(new Uint8Array([0x61, 0x62, 0x63, 0x64]); // abcd
string_t[4].decode(new Uint8Array([0x61, 0x62, 0x00, 0x64]); // ab

bits

import { DWORD, bits, StructBuffer } from "struct-buffer";

const EFLAG_DATA = 0x00000246;
const littleEndian = true;
const EFLAG = bits(DWORD, {
  CF: 0,
  PF: 2,
  AF: 4,
  ZF: 6,
  SF: 7,
  TF: 8,
  IF: 9,
  DF: 10,
  OF: 11,
});

// decode
const data = EFLAG.decode(new Uint32Array([EFLAG_DATA]), littleEndian);
// => { CF: 0, PF: 1, AF: 0, ZF: 1, SF: 0, TF: 0, IF: 1, DF: 0, OF: 0 }

// encode
const view = EFLAG.encode(
  {
    PF: 1,
    ZF: 1,
    IF: 1,
  },
  littleEndian
);
// => <44 02 00 00>

bitFields

import { uint8_t, bitFields, StructBuffer, sbytes as b, } from "struct-buffer";

const bf = bitFields(uint8_t, {
  a: 1,
  b: 2,
  c: 3,
});

const v = bf.encode({
  a: 1,
  b: 2,
  c: 3,
});
// => <1D>

const data = bf.decode(b("1D"));
// => { a: 1, b: 2, c: 3 }

pack and unpack

import { pack, pack_into, unpack, unpack_from, iter_unpack, calcsize, Struct, sbytes as b } from "struct-buffer";

pack("b2xb", 2, 1)
// => <02 00 00 01>

unpack("b2xb", b("02 00 00 01"))
// => [ 2, 1 ]

calcsize("hhl")
// => 8


const [hp, mp, name] = unpack(
  ">II3s",
  b("00 00 00 64 00 00 00 0A 61 62 63")
);
expect(hp).toBe(100);
expect(mp).toBe(10);
expect(name).toBe('abc');

Note: Without "@, =, P", the default byte order is ">"

Some utility functions

import { createDataView, makeDataView, sbytes as b, sbytes2 as b2, sview, TEXT } from "struct-buffer";

createDataView(3)
// => <00 00 00>

makeDataView([1, 2, 3])
// => <01 02 03>

b("01 02 03")
// => <01 02 03>

b2("abc\\x1\\x2\\x3")
// => <61 62 63 01 02 03>

TEXT(pack("3s2b3s2I", "abc", 1, 2, "xyz", 8, 9))
// => "abc..xyz........"

test

$ npm test

build

$ npm run build

See also:

• See the test for more examples
• DataView
• C_data_types
• Built-in types (C++)
• C++ Bit Fields